WO2003002949A2

WO2003002949A2 - Capacitive measuring system

Info

Publication number: WO2003002949A2
Application number: PCT/FR2002/002234
Authority: WO
Inventors: Claude Launay; Pascal Jordana; Daniel Le Reste; William Panciroli; Joachim Da Silva; Philippe Parbaud
Original assignee: Hitachi Computer Products (Europe Sa)
Priority date: 2001-06-28
Filing date: 2002-06-27
Publication date: 2003-01-09
Also published as: JP2004530907A; JP4307248B2; US20050068043A1; FR2826723B1; FR2826723A1; EP1399714A2; WO2003002949A3; CA2451961A1; US7098673B2

Abstract

The invention relates to a measuring device comprising at least one measuring probe (10), means for sequentially applying a controlled supply voltage between the measuring probe (10) and a reference element, and means for integrating accumulated electric charges on the measuring probe (10), characterized in that said device also comprises at least one auxiliary measuring probe (100) which is also sequentially linked to controlled electric supply means and to charge integrating means, said auxiliary measuring probe (100) having a capacity, in relation to a potential detection zone, which is different from the main measuring probe (10), whereby comparative utilization of signals respectively emitted by the two measuring probes (10,100) enables the influence of the main measuring probe to be determined.

Description

CAPACITIVE MEASUREMENT SYSTEM

The present invention relates to the field of sensors. More specifically, the present invention relates to a measurement device exploiting an indirect measurement of permittivity between two electrically conductive bodies respectively forming a measurement probe and a reference element, for example a reference probe.

Document WO-0025098 describes a device, the basic structure of which is shown diagrammatically in FIG. 1 attached.

This device comprises two electrically conductive bodies constituting respectively a measurement probe 10 and a reference probe 20, electrical supply means 30 capable of delivering a continuous electrical voltage of controlled amplitude, an integrating stage 50 comprising a switching system of capacity 53 and control means 40 adapted to define cyclically, at a controlled frequency, a series of two sequences: a first sequence T1 during which the electrical supply means 30 are connected to the measurement probe 10 to apply a electric field between the measurement probe 10 and the reference probe 20 and accumulate electrical charges on the measurement probe 10, then a second sequence T2 during which the electrical supply means 30 are disconnected from the measurement probe 10 and this is connected to a summing point of the integrating stage 50 to transfer loads da ns the integrator stage 50 and obtain at the output thereof a signal representative of the permittivity existing between the measurement probe 10 and the reference probe 20.

More precisely still, according to document WO-0025098, the integrator stage 50 comprises an operational amplifier 51, a first integration capacitor 52 mounted in feedback on this amplifier 51 and a second capacitor 53 switched between the output and the input of the operational amplifier 51 at the rate of the sequences controlled by the control means 40, so that, at an established equilibrium regime, a voltage is obtained at the output of the operational amplifier 51 with equilibrium equal to -E.Cs / C53, relationship in which -E denotes the amplitude of the voltage across the terminals of the power supply means 30 and Cs and C53 denote respectively the values of the capacities defined between the measurement probe 10 and the reference probe 20 on the one hand, and the second switched capacitor 53 on the other hand.

The switching of the electrical supply means 30 and of the second capacitor 53 is ensured by reversing switches 42, 43 controlled by a time base 41.

The operation of this known device is essentially as follows.

Suppose that at the outset the integration capacitor C52, the switching capacitor C53 and the capacitor Cs formed between the measurement probe 10 and the reference probe 20 are each fully discharged, ie QC52 = 0 QC53 = 0, and QCs = 0.

During the first sequence T1, the capacitor Cs is charged under the supply voltage delivered by the module 30, which is assumed here to be equal to -E.

At the end of the T1 sequence, we therefore have: QCs = -E.Cs QC52 = 0 QC53 = 0. During the following T2 sequence, the charges are transferred from Cs to C52; either, the charges being preserved and Cs and C53 being connected to the inverting input of the operational amplifier 51 of zero virtual impedance:

-E.Cs = Vs2.C52, by calling Vs2 the output voltage of the operational amplifier 51 during the sequence T2.

During the following sequence T1, the two capacitors C52 and C53 are placed in parallel. We then have: Vs = Vs2.C52 / (C52 + C53) = QC53 / C53 = QC52 / C52, i.e. QC53 = [Vs2.C52 / (C52 + C53)]. C53

= [Vs2 /(1+C53/C52).C53 or if C52 = nC53 »C53 QC53 _z Vs2.C53.

In the following sequence T2, the charges contained in C53 come in opposition to those Cs. The remaining part of the Cs charges is transferred to C52, etc.

The output voltage Vs, at the output of the operational amplifier 51 increases progressively until a voltage Vs equilibrium = QC53 / C53 such that QC53 = Vs equilibrium.C53 = -E.Cs.

Thus after x iterations the device reaches an equilibrium regime on the point of summation. The QC53 charges of C53 compensate for the charges of the Cs probe.

As soon as a variation in capacity Cs is detected, the additional (or loss) of charges on Cs will charge (or discharge) the capacity C52.

Thus in steady state the switching capacity C53 balances the variations in charges of the probe Cs. The present invention now aims to provide a new device incorporating the concept described in document WO-0025098, but having higher performance than that of known prior devices.

More specifically, the present invention aims to propose new means for better identifying the environment of the measurement probe, to improve the detection of a transient phenomenon, for example eliminating the effect of an obstacle permanent interposed between the measurement probe and the zone of appearance of a transient phenomenon. In this context, the present invention can find in particular, but not exclusively, application in the detection of a person or an object on a seat of a motor vehicle. This object is achieved in the context of the present invention thanks to a device comprising at least one main measurement probe, means capable of sequentially applying a controlled supply voltage between the main measurement probe and a reference element and means able to integrate the electrical charges accumulated on the main measurement probe, characterized in that it also comprises at least one auxiliary measurement probe, also connected sequentially to means of controlled electrical supply and to integration means of loads, the said auxiliary measurement probe having, with respect to a potential detection area, a different capacity from the main measurement probe, so that the comparative exploitation of the signals originating respectively from the two measurement probes allows determine the influence of the main measuring probe.

According to a first embodiment of the present invention, the auxiliary measurement probe has a small controlled area compared to the main measurement probe.

According to a second embodiment of the present invention, the auxiliary measurement probe is located at a distance from the potential detection zone, different from the main measurement probe. According to a third embodiment of the present invention, the auxiliary measurement probe is located in the same plane at a distance from the reference element different from the main measurement probe.

Other characteristics, objects and advantages of the present invention will appear on reading the detailed description which follows and with reference to the appended drawings given by way of nonlimiting examples and in which: FIG. 1 previously described schematically represents a device in accordance with the state of the art disclosed in document WO-0025098, FIG. 2 schematically represents the detection of a passenger in a vehicle seat, using measurement probes in accordance with document WO-0025098, FIG. 3 diagrammatically represents the same device in the case of an obstacle interposed between the measurement probes and the detected body, FIG. 4 diagrammatically represents, in a plan view, a main measurement probe and an auxiliary measurement probe, in accordance with a first embodiment of the present invention, FIG. 5 shows the same main and auxiliary measurement probes in accordance with a first embodiment of the present invention, in the case of the detection of a body with a surface different from FIG. 4, FIG. 6 schematically represents, in a sectional view, a main measurement probe and an auxiliary measurement probe, in accordance with a second embodiment of the present invention,

FIGS. 7 and 8 schematically represent, respectively in a sectional view and a plan view, a main measurement probe and an auxiliary measurement probe, in accordance with a third embodiment of the present invention,

- Figures 9 and 10 schematically represent an example of supply of the measurement probes illustrated in Figures 7 and 8 and the resulting detection, - Figure 11 shows a plan view of probes according to another alternative embodiment of the present invention,

FIG. 12 represents a plan view on an enlarged scale in the transverse direction and compressed in the longitudinal direction of the same probes,

FIG. 13 represents a cross-sectional view of the same probes and illustrates more precisely the field lines according to a particular implementation, and

FIG. 14 illustrates a diagram of results obtained using the probes illustrated in FIGS. 11 to 13, which diagram makes it possible to discriminate between different detection configurations. For simplification purposes, the detailed description which follows will be made with reference to the detection of a person on a seat of a motor vehicle. However, the present invention is not limited to this particular application.

FIG. 2 shows diagrammatically two measurement probes 10 integrated in the seat 90 of a motor vehicle seat for the possible detection of a person P.

As described in document WO-0025098, the detection of the person P can be carried out by sequentially applying a controlled electrical voltage between the measurement probes 10 and a reference element, such as the chassis of the motor vehicle, then integrating the loads thus accumulated on the measurement probes 10.

As a variant, the two probes referenced 10 in FIG. 2 can serve one as a measurement probe and the other as a reference element.

The same measurement probes 10 for the detection of the same person P have been shown diagrammatically in FIG. 3, but in the case where an obstacle O, such as a mat of balls or a towel, is interposed between the seat cushion , and therefore probes 10, and person P.

Those skilled in the art will understand that such an obstacle increases the distance between the probes 10 and the person P (this distance goes from e1 to e2), consequently decreases the output signal of the detection device defined in the document WO -0025098.

Without particular precautions, such an obstacle O therefore risks distorting the detection, by assimilating the person P to a mass less than that of FIG. 2.

As indicated above, the object of the present invention is to propose means making it possible to eliminate this difficulty.

According to a first embodiment shown diagrammatically in FIGS. 4 and 5, it is provided in the context of the present invention, an auxiliary measurement probe 100 having a surface area significantly smaller than that of the main measurement probe. According to the representation given in FIGS. 4 and 5, the auxiliary measurement probe has a square outline. The invention is however not limited to this particular arrangement. The auxiliary measurement probe 100 may take any other appropriate geometry, such as for example a circular contour.

The auxiliary measurement probe 100 is located at the same distance from the potential detection zone, for example the upper surface of a seat, as the main measurement probe 10.

The surface and the location of the auxiliary measurement probe 100 are such that it always experiences the same external influence during the appearance of a transient external phenomenon, whatever the amplitude of this phenomenon. For example, in the case of the detection of a person P, the surface and the location of the auxiliary measurement probe 100 are such that it is always located entirely under the person P when the latter takes place on the seat.

On the other hand, the surface and the location of the main measurement probe 10 are such that the surface of this main measurement probe 10 influenced by the transient external phenomenon, depends on the amplitude of this phenomenon, for example in the case of detection. of a person in a motor vehicle seat, depends on the body size of the person P. By way of nonlimiting example, the auxiliary measurement probe 100 can be centered on the detection zone, have a greater transverse dimension of the order of a few centimeters, for example less than 3 cm, preferably less than 1 cm and a total area less than a few square centimeters, for example less than 9 cm ² , preferably less than 4 cm ² .

On the contrary, the main measurement probe 10 preferably has at least one dimension greater than the largest possible dimension of the body P capable of being detected.

The main measurement probe 10 can be of any geometry such as for example sinusoidal or rectangular. In the latter case, it develops a surface of the order of a few cm over several dm, for example of the order of a few cm, such as of the order of 5 cm, over more than 30 cm, preferably more than 40 cm. The use of the auxiliary electrode illustrated in FIGS. 4 and 5 makes it possible to standardize the measurement as a function of the distance from the body P.

In fact, the exploitation of the signal resulting from the integration of the charges accumulated on the auxiliary measurement probe 100 makes it possible to know the distance separating the body P from the auxiliary measurement probe 100, since the importance of the body P has no influence on This measure.

On the other hand, the exploitation of the signal resulting from the integration of the charges accumulated on the main measurement probe 10, normalized by the result coming from the auxiliary measurement probe 100, makes it possible to have direct reliable information representative of the importance from the body

P.

According to a second embodiment shown diagrammatically in FIG. 6, there is provided in the context of the present invention, an auxiliary measurement probe 100 located at a distance from the potential detection zone, for example the upper surface of a seat of seat, different from the main measurement probe 10, but preferably having an area identical to that of the main measurement probe. The auxiliary measurement probe 100 is also close to the main measurement probe 10.

The distance between the two probes 100 and 10 from the body to be detected must be constant.

Thus the difference in influence of the body P respectively on the two probes 10 and 100 depends only on the difference in distance between the body P and these probes 10 and 100. If we call:. S1 the surface of the main measurement probe 10,. S2 the surface of the auxiliary measurement probe 100,. e the distance separating the measurement probe 10 and the body P, and. at the additional distance separating the main measurement probe 10 and the auxiliary measurement probe 100, relative to the body P, we obtain:

. on the main measurement probe 10, a capacity C1 = K (S1 le) and. on the auxiliary measurement probe 100, a capacity C2 = K [S2 / (e + a)]. The combination of the two preceding expressions therefore makes it possible to know the distance e and to get rid of it later in the measurement.

Obviously, a similar detection can be obtained with measurement probes 10 and 100 of any geometry and of surfaces S1 and S2 different, but of known ratio, positioned at a relative distance also known.

As indicated previously for FIGS. 4 and 5, the main measurement probe 10 preferably has at least one dimension greater than the largest possible dimension of the body P capable of being detected. The main measurement probe 10 can also comply with the provisions described above with reference to FIGS. 4 and 5.

According to a third embodiment shown schematically in Figures 7 to 10, there is provided in the context of the present invention, a main measurement probe 10 and an auxiliary measurement probe 100 placed at a different distance (asymmetrical) relative to a reference element

110.

Thus, depending on the active measurement probe, 10 or 100, the distribution of the electric field varies (see in particular Figures 9 and 10) and therefore the influence of the body P to be detected as a function of the distance on this same probe changes.

It is therefore possible to determine the distance e separating the body to be detected P from the measurement probes 10 and 100, by a combined exploitation of the signals coming from these two measurement probes 10 and 100, for example by a ratio of the two capacitors C1 and C2 measured on these two probes.

By way of nonlimiting example, as illustrated in FIGS. 7 and 8, the two measurement probes, main 10 and auxiliary 100, can be coplanar with the reference element 110. According to the nonlimiting representation given in FIGS. 7 at 10, the auxiliary probe 100 is located between the measurement probe 10 and the reference element 110. Typically the center distance 11 between the two measurement probes 10 and 100 is of the order of a few millimeters, and the center distance 12 between auxiliary probe 100 and the reference element 110 is of the order of a few centimeters but at least twice its size.

The main 10 and auxiliary 100 measurement probes preferably have identical surfaces, but can be of any geometry, for example rectangular. The reference element 110 can also have a surface identical to the main 10 and auxiliary 100 measurement probes. However as a variant, the main 10 and auxiliary 100 measurement probes can have different surfaces of known ratio. Again, the main measurement probe 10, at least, preferably has at least one dimension greater than the largest possible dimension of the body P capable of being detected.

As shown diagrammatically in FIGS. 9 and 10, when one of the two probes 10 or 100 is active, the other probe 100 or 10 can itself serve as an auxiliary reference element.

It will be recalled that in the context of the present invention, the main 10 and auxiliary 100 measurement probes are each sequentially connected to a source of electrical power of known amplitude and then the electrical charges accumulated on these probes are integrated, preferably with means comparable to those defined in the document

WO-0025098 (and described with reference to Figure 1). The power supply means and the charge integration means can be the same for the different probes 10 and 100. In this case switching / multiplexing means alternately switch the probes 10 and 100 at the terminals of these means. As a variant, it is possible to provide electrical supply means and means for integrating different charges for the various probes 10 and 100.

In the context of the present invention, the reference element can be formed of a reference probe or of a mass constituted for example by the earth or a neighboring metallic mass, for example the chassis of a motor vehicle.

Those skilled in the art will understand that the various embodiments in accordance with the present invention, previously described, allow two independent measurements to be made with each other, under the same conditions, of the same transient phenomenon, and therefore to decouple the two influence phenomena that are the surface and the distance of the body P to be detected. Of course the present invention is not limited to the particular embodiments which have just been described but extends to any variant in accordance with its spirit.

The present invention can relate to a large number of applications. We previously mentioned the detection of the presence of a user on a motor vehicle seat, in particular for the control of an airbag system. However, the present invention is not limited to this particular application. The present invention may for example also relate, inter alia, to anti-intrusion detection fields or even fluid level detectors. We will now describe the alternative embodiment according to the present invention illustrated in Figures 11 to 13 attached.

We find in these figures three probes referenced respectively 10, 100 and 110.

The functions of these three probes 10, 100 and 110 may vary depending on the configuration of use.

In principle, the probe 110 serves as a reference probe. In this context, the probe 10 constitutes the main measurement probe, while the probe 100 constitutes the auxiliary measurement probe.

However, during another operating phase in accordance with the present invention, the probe 10 can constitute the main measurement probe, while the probe 100 serves as a reference probe.

According to the embodiment shown in Figures 11 to 13, each probe 10, 100 and 110 is elongated. Its length L is typically greater than 10 times its width, very preferably its length L is typically greater than 20 times its width.

According to a first notable characteristic of the embodiment shown in FIGS. 11 to 13, the probe 100 has a U-shaped configuration. Thus the probe 100 comprises two main strands 102, 104, parallel between them and arranged respectively on either side of the probe 10. In other words, the probe 100 frames the probe 10. To this end, on one of their ends, the two strands 102, 104 are connected between them by a connecting element 103. The Applicant has determined that, thanks to the above characteristics, the electrode 10 is very insensitive to the edge effects of the electric field and only gives signal information when the passenger is very close to the probe. On the other hand, the electrode 100 is very sensitive to the edge effects of the electric field and gives signal information even when the passenger is very far from the probe (for example typically up to twenty centimeters from the probe).

According to a second important characteristic of the embodiment shown in FIGS. 11 to 13, the probe 10 and the probe 100 have varying widths along their length. More precisely still, preferably, each of the probes 10 and

100 comprises three sections: a central section 16, 106 and two end sections 18,19; 108, 109.

Preferably, the end sections 18, 19 on the one hand, and 108, 109 on the other hand, have identical widths for a given probe 100 or 200.

More precisely still, preferably, the probe 100 comprises a central section 16 of length L16 and of great width £ 16 and two end sections 18, 19 of length L18 and L19 of small width £ 18, £ 19 less than £ 16 . Typically but not limited to £ 16 = 4 £ 18 = 4 £ 19.

Furthermore, typically L16 = 2L18 = 2L19.

Preferably, the probe 100 comprises a central section 106 of length L106 and of small width £ 106 and two end sections 108, 109 of length L108, L109 and of wide width £ 108, £ 109 greater than £ 106.

Typically £ 108 = £ 109 = 2 £ 106 = 2 £ 18 = 2 £ 19. Typically L106 = 2L108 = 2L109.

Thanks to the geometric characteristics which have just been mentioned, when a voltage is applied alternately or simultaneously between the probes 10 and 110 on the one hand, 100 and 110 on the other hand, the probe 10 is very sensitive to a centered external element. , that is to say placed opposite the central section 16 while the probe 100 is very sensitive to an off-center element, that is to say an element placed opposite the end sections 108, 109.

According to a third notable characteristic of the invention illustrated in FIGS. 11 to 13, each probe 10, 100 and 110 is non-rectilinear. In this case, each probe 10, 100, 110 is formed of different segments, rectilinear individually, connected in pairs by their ends by transition elements made up of dihedrons whose concavities are alternated, that is to say oriented alternately in one direction then in the other. Thus, the probes 10, 100 and 110 are in the form of zig zag undulations.

Such a geometry allows elongation by deformation of the support.

This characteristic is particularly important when the probes 10, 100 and 110 are integrated in a vehicle seat. Indeed, this geometry allows an extension of the probes when a driver or passenger takes place on the seat.

It will also be noted that preferably, the distance which separates the probe 110 from the probe 10 or from the probe 100 is greater than the distance which separates the probes 10 and 100 between them.

In addition, the supply voltage application means are adapted to apply a voltage sequentially between the probes 10 and 100 in an operating phase, and between the probe 110 and each of the two probes 10 and 100 during a other operating phase. In FIG. 13, the field lines obtained during the application of a voltage between the probes 10 and 100 are referenced C1 while the field lines obtained during the application of a voltage between the probe 110 and each of the two probes 10 and 100 are referenced C2. On examining FIG. 13, it can be seen that when a voltage is applied between the probes 10 and 100, the detection range is very reduced because the field lines C1 are strongly curved.

On the contrary, when the voltage is applied between the probe 110 and each of the probes 10 and 100, the detection range is much greater since the field lines C2 are substantially orthogonal to the supports of the probes.

By way of nonlimiting example, the probe 110 can be placed approximately 2 cm from the probes 10 and 100. As indicated above in the context of the present invention, the signals from the various probes are used in a comparative manner. .

In the context of the embodiment represented in FIGS. 11 to 13, it is thus possible to compare the signals obtained on the probes 10 and 100, the signals obtained by summation on the two probes 10 and 100 with the signal of the probe 10 or with the signal of probe 100, etc ...

Those skilled in the art will understand that the present invention thus offers a large number of comparison choices.

More precisely still, and without limitation, the present invention can for example exploit one of the following relationships:

. U / C, U representing the signal taken from the probe 100 during the application of a supply voltage between, on the one hand the probes 10 and 110 connected together and serving as a reference probe, and on the other hand share the probe 100, while C represents the signal taken from the probe 10 during the application of a supply voltage between on the one hand the probes 100 and 110 connected together and serving as a reference probe, and d on the other hand the probe 10,

. UC / C, UC representing the signal taken from the probe 100 during the application of a supply voltage between the probe 110 and simultaneously the probes 10 and 100.. UA / U, . CU / U, CU representing the signal taken from the probe 10 during the application of a supply voltage between the probe 110 and simultaneously the probes 10 and 100,. CU / U. By way of nonlimiting example, the comparison of the summation of the signals UC + CU defined previously, with the signal C defined previously, which corresponds to the diagram illustrated in FIG. 14, makes it possible to discriminate four zones:

- a zone A which corresponds to an absence of an element of external influence, for example an empty seat,

- a zone B which corresponds to an environment without wet obstacle, for example an occupied seat without wet obstacle,

a zone C which corresponds to an environment occupied with a wet obstacle, for example a seat occupied with a wet obstacle, and a zone D of an environment occupied at a distance, for example a seat occupied with a passenger distant from the seat.

Of course the present invention is not limited to this particular operating mode and extends to any variant in accordance with its spirit.

Claims

1. Measuring device comprising at least one measuring probe (10), means (30) capable of sequentially applying a controlled supply voltage between the measuring probe (10) and a reference element (20) and means (50) capable of integrating the electrical charges accumulated on the measurement probe (10), characterized in that it also comprises at least one auxiliary measurement probe (100), also connected sequentially to electrical supply means controlled (30) and to charge integration means (50), said auxiliary measurement probe (100) having, with respect to a potential detection area, a capacity different from the main measurement probe (10) , so that the comparative analysis of the signals originating respectively from the two measurement probes (10, 100) makes it possible to determine the influence of the main measurement probe.

2. Device according to claim 1, characterized in that the auxiliary measurement probe (100) has a small controlled area compared to the main measurement probe (10).

3. Device according to claim 2, characterized in that the auxiliary measurement probe (100) is located at the same distance from the potential detection area, for example the upper surface of a seat, as the main measurement probe (10).

4. Device according to one of claims 2 or 3, characterized in that the surface and the location of the auxiliary measurement probe (100) are such that it always experiences the same external influence when the appearance of 'a transient external phenomenon, whatever the amplitude of this phenomenon.

5. Device according to one of claims 2 to 4, characterized in that the surface and the location of the main measurement probe (10) are such that the surface of this main measurement probe (10) influenced by the phenomenon transient exterior, depends on the amplitude of this phenomenon.

6. Device according to one of claims 2 to 5, characterized in that the auxiliary measurement probe (100) is centered on the detection zone.

7. Device according to one of claims 2 to 6, characterized in that the auxiliary measurement probe (100) has a larger transverse dimension of the order of a few centimeters, for example less than 3 cm, preferably less than 1cm.

8. Device according to one of claims 2 to 7, characterized in that the auxiliary measurement probe (100) has a total area less than a few square centimeters, for example less than 9 cm ² , preferably less than 4 cm ² .

9. Device according to one of claims 2 to 8, characterized in that it comprises means capable of exploiting the signal resulting from the integration of the charges accumulated on the auxiliary measurement probe (100) to determine the distance separating a body (P) of the auxiliary measurement probe (100), then normalize the measurement obtained from the main probe (10) accordingly.

10. Device according to claim 1, characterized in that the auxiliary measurement probe (100) is located at a distance from the potential detection zone, different from the main measurement probe (10).

11. Device according to claim 10, characterized in that the auxiliary measurement probe (100) has a surface identical to that of the main measurement probe (10).

12. Device according to claim 10, characterized in that the auxiliary measurement probe (100) has a surface different from that of the main measurement probe (10), but with a known ratio with respect thereto.

13. Device according to one of claims 10 to 12, characterized in that the auxiliary measurement probe (100) is close to the main measurement probe (10), so that the influence difference of a external body (P) respectively on the two probes (10, 100) depends only on the distance difference between the body (P) and these probes (10, 100).

14. Device according to one of claims 10 to 13, characterized in that it comprises means able to combine the signals detected on the two measurement probes (10, 100) to know the distance (e) between the probe main (10) and a body to be detected (P) and to get rid of it later in the measurement.

15. Device according to claim 1, characterized in that the auxiliary measurement probe (100) and the main measurement probe (10) are asymmetrical with respect to a reference element (110).

16. Device according to claim 15, characterized in that the auxiliary measurement probe (100) is located at a distance from the reference element (110) different from the main measurement probe (10).

17. Device according to one of claims 15 or 16, characterized in that it comprises means capable of determining the distance (e) separating a body to be detected (P) from the measurement probes (10, 100), by a combined exploitation of the signals from these two measurement probes (10, 100), for example by a ratio of the two capacities measured on these two probes.

18. Device according to one of claims 15 to 17, characterized in that the two measurement probes, main (10) and auxiliary (100), are coplanar with the reference element (110).

19. Device according to one of claims 15 to 18, characterized in that the main (10) and auxiliary (100) measurement probes have identical surfaces, for example rectangular.

20. Device according to one of claims 15 to 19, characterized in that the reference element (110) has a surface identical to the main (10) and auxiliary (100) measurement probes.

21. Device according to one of claims 15 to 18, characterized in that the main (10) and auxiliary (100) measurement probes have different surfaces of known ratio.

22. Device according to one of claims 15 to 21, characterized in that when one of the two measurement probes (10, 100) is active, the other measurement probe (100, 10) itself serves to auxiliary reference element.

23. Device according to one of claims 1 to 22, characterized in that the main measurement probe (10) has at least one dimension greater than the largest possible dimension of the body P capable of being detected.

24. Device according to one of claims 1 to 23, characterized in that it comprises a probe (100) of U-shaped configuration comprising two main strands (100, 204) parallel to each other arranged on each side respectively another probe (10).

25. Device according to one of claims 1 to 24, characterized in that it comprises at least one probe (10, 100) having a changing width over its length.

26. Device according to claim 25, characterized in that it comprises at least one probe (10, 100) comprising three sections: a central section (16, 106) and two end sections (18, 19; 108, 109).

27. Device according to one of claims 25 or 26, characterized in that it comprises at least one probe (10) comprising a central section (16) of great width (£ 16) and two end sections (18 , 19) of small width (£ 18, £ 19).

28. Device according to one of claims 25 to 27, characterized in that it comprises at least one probe (100) comprising a central section (106) of small width (106 pounds) and two end sections (108 , 109) wide (£ 108, £ 109).

29. Device according to one of claims 1 to 28, characterized in that it comprises at least one non-rectilinear probe (10, 100, 110).

30. Device according to claim 29, characterized in that it comprises at least one probe (10, 100, 110) consisting of different rectilinear segments connected in pairs by their ends by transition elements of dihedral type concave to concavity alternately.

31. Device according to one of claims 1 to 30, characterized in that it comprises a first set of two probes (10, 100) located at a determined distance from one another and a third probe (110 ) situated at a distance from the two first named probes (10, 100) greater than the spacing between them.

32. Device according to claim 31, characterized in that it comprises means capable of sequentially applying a voltage between the two first named probes (10, 100) on the one hand, and on the other hand between the third probe ( 110) and respectively each of the two first named probes (10, 100).

33. Device according to one of claims 1 to 32, characterized in that it comprises two electrically conductive bodies constituting respectively the measurement probe (10) and the reference element (20), electrical supply means (30) capable of delivering a continuous electrical voltage of controlled amplitude, an integrating stage (50) comprising a capacity switching system (53) and control means (40) adapted to define cyclically, at a controlled frequency, a following two sequences (T1, T2): a first sequence during which the power supply means (30) are connected to the measurement probe (10) to apply an electric field between the measurement probe (10) and the reference element (20) and accumulate electrical charges on the measurement probe (10), then a second sequence during which the electrical supply means (30) are disconnected from the measurement probe (10) e t the latter is connected to a summing point of the integrating stage (50) to transfer charges into the integrating stage (50) and to obtain at its output a signal representative of the permittivity existing between the measurement (10) and the reference element (20), the integrator stage (50) further comprising an operational amplifier (51), a first integration capacitor (52) mounted in feedback on this amplifier (51) and a second capacitor (53) switched between the output and the input of the operational amplifier (51) at the rate of the sequences (T1, T2) controlled by control means (40), so that in steady state established, one obtains at the output of the operational amplifier (51), a voltage "Vs balance" equal to:

- Ecs / C53, relationship in which -E designates the amplitude of the voltage across the power supply means (30), and Cs and C53 designate respectively the values of the capacities defined between the measurement probe (10) and the reference element on the one hand and the second switched capacitor (53) on the other hand.